Method of selectively bonding braze powders to a surface

ABSTRACT

A method for selectively adhering braze powders to a surface comprises applying a braze powder to a surface, and then directing a laser beam onto the braze powder while the laser beam moves along a predetermined path relative to the surface. The laser beam selectively heats the braze powder along the predetermined path such that the braze powder is sintered and bonded to the surface. Thus, a braze deposit is formed at one or more predetermined locations on the surface. After forming the braze deposit, excess braze powder, that is, the braze powder not selectively heated by the laser, is removed from the surface.

TECHNICAL FIELD

The present disclosure relates generally to applying braze powders to surfaces, and more particularly to a method of selectively sintering and adhering braze powders to one or more predetermined locations on a surface.

BACKGROUND

Gas turbine engines include a compressor, combustor and turbine in flow series along a common shaft. Compressed air from the compressor is mixed with fuel in the combustor to generate hot combustion gases that rotate the turbine blades and drive the compressor. In a conventional turbine compressor, turbine blades may be fabricated separately from the rotor disk and then mechanically assembled such the turbine blades extend from machined slots on the disk; however, this configuration has the disadvantage of discontinuities between the blades and the disk. To eliminate such discontinuities, diffusion bonding techniques have been developed to bond the turbine blades to the disk to form a mechanically robust, monolithic component (a “turbine blisk”). Diffusion bonding is a solid-state bonding method, where elevated temperatures and typically high pressures are employed to obtain diffusion of atoms between mating components, allowing for formation of a thermally-stable metallurgical bond. Various gas turbine engine components may benefit from diffusion bonding.

Diffusion bonding may be facilitated or improved by utilizing diffusion agents or braze materials, such as braze foils or powders, between the components to be joined. However, the bonding of components having complex surface geometries can present challenges with the use of such diffusion agents. For example, the use of braze foils may not be effective for irregular or discontinuous surfaces, and it may be difficult if not impossible to deposit consistent levels of braze powder on such surfaces using methods known in the art. In addition, conventional methods of braze powder application, which typically provide blanket surface coverage of costly braze alloys, may lead to waste and/or bonding problems when a braze deposit is needed only for selected areas.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may be better understood with reference to the following drawing(s) and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views.

FIGS. 1A-1D are cross-sectional schematics illustrating a laser-based method of selectively sintering and bonding braze powders to a surface.

FIGS. 1E and 1F illustrate diffusion bonding of the surface to a mating surface.

FIG. 2 shows an exemplary assembly for diffusion bonding comprising a spar and a cover sheet.

DETAILED DESCRIPTION

FIGS. 1A-1D illustrate a laser-based method for selectively sintering and adhering braze powders to a surface of a first component. The method may be useful to form a braze deposit at selected location(s) on the surface prior to diffusion bonding the first component to a second component, as discussed below.

Referring to FIG. 1A, the method entails applying a braze powder 106 onto a surface 104. Typically, the braze powder 106, which comprises a metal alloy (or “braze alloy”) as described below, is applied to the surface 104 by spraying, scattering, or dusting. Some or all of the surface 104 may be completely covered by the braze powder 106 to ensure that adjacent particles of the braze powder 106 are in physical contact to facilitate sintering in the next step. The braze powder may be applied to the surface in an amount sufficient to achieve a predetermined thickness or mass density. For example, the mass density of the braze powder 106 may lie in a range from about 0.04 g/in² to about 0.25 g/in², or in some cases from about 0.06 g/in² to about 0.08 g/in². Prior to applying the braze powder 106, the surface 104 may undergo standard surface preparation procedures, such as cleaning and/or grinding, to remove contaminants such as dust, chemical residues, and oxides.

FIG. 1B illustrates the use of a laser to selectively sinter and adhere the braze powders to the surface 104. A laser beam 108 is directed onto the braze powder 106 while moving along a predetermined path 110 over the surface 104; consequently, the braze powder 106 within the predetermined path 110 is selectively heated. More specifically, only the braze powder 106 falling within the predetermined path 110 of the laser beam 108 is heated. This selective heating causes the braze powder 106 to sinter and adhere to the surface 104 along the predetermined path 110, as illustrated in FIGS. 1B and 1C. Thus, a braze deposit 112 is formed at one or more predetermined locations on the surface 104.

The method may further include, after forming the braze deposit 112, removing the braze powder 106 from any portion of the surface 104 not along the predetermined path 110. In other words, the braze powder 106 that is not heated by the laser, and which may be considered to be excess braze powder, may be removed from the surface 104 after forming the braze deposit 112, such that only the braze deposit 112 remains, as shown in FIG. 1D. To remove the excess braze powder, the surface 104 may be vibrated, overturned, washed, brushed, or sprayed with a gas or liquid.

Returning to FIG. 1B, the predetermined path 110 followed by the laser beam 108 may be a continuous path along the surface 104. Alternatively, the predetermined path may be a discontinuous path where the laser beam is operated intermittently (turned off and on) while moving. Similarly, the surface may be a continuous surface or a discontinuous surface that includes surface regions separated by gaps or holes. In the latter case, the laser beam may be operated intermittently to selectively heat the braze powder on the surface regions, thereby forming a braze deposit only on the surface regions.

It should be understood that references to the laser beam 108 moving over the surface 104 are intended to broadly describe relative motion between the laser beam 108 and the surface 104, and thus may encompass any of the following situations: (1) the laser beam 108 moving while the surface 104 remains stationary; (2) the laser beam 108 remaining stationary while the surface 104 moves; and/or (3) the laser beam 108 moving while the surface 104 also moves. The relative motion between the laser beam 108 and the surface 104 may be electronically controlled in three dimensions (along x- y- and/or z-axes), and the path 110 of the laser beam 108 may be programmed.

The laser beam 108 may be generated by a commercially available laser such as a gas laser (e.g., CO₂ laser), a solid state laser (e.g., a Nd:YAG or Nd:YVO₄ laser), or a fiber laser. The laser beam 108 may be a pulsed laser beam or a continuous laser beam. Advantageously, the laser beam is operated at a power level and scan rate sufficient to sinter the braze powder 106 without inducing melting. Accordingly, the braze powder 106 along the predetermined path 112 may be heated to a sintering temperature that is below a solidus of the braze alloy, where the solidus is the highest temperature at which the braze alloy is completely solid. For example, the sintering temperature may be in a range from about 400° C. to about 800° C. In some cases, during sintering of the braze powder, there may be some partial melting, but the braze powder is preferably not fully liquified during laser heating. A suitable power level for the laser beam may lie in a range from about 100 W to about 500 W, depending on the braze alloy. At higher power levels, the laser beam may be moved relative to the surface at a faster scan rate to control the heating.

As indicated above, the surface 104 is part of a first component 120 which may undergo diffusion bonding to a second component 122, as will be discussed below in reference to FIGS. 1E and 1F. Both the first and second components 120,122 may comprise a metal alloy which may be suitable for high temperature applications, such as a nickel-base alloy, a titanium-base alloy (e.g., a titanium aluminide), or an iron-base alloy.

The braze powder 106 comprises a metal alloy or braze alloy selected at least in part based on the metal alloy(s) present at mating surfaces of the first and second components 120,122. For example, the braze powder 106 may comprise a nickel-based braze alloy, a titanium based-braze alloy, or an iron-based braze alloy. Suitable nickel-based braze alloys may include nickel alloyed with boron, chromium, manganese, and/or silicon. Suitable titanium-based braze alloys may include titanium alloyed with copper, nickel and/or zirconium. Commercially available braze powder 106 may be employed. The braze powder 106 may include particles of a spheroidal, spherical, polygonal, elongated, irregular, or other morphology. Typically, the particles have a nominal size (e.g., width or diameter) in the range of tens or hundreds of microns.

Referring to FIGS. 1E and 1F, a method of diffusion bonding comprises assembling a first component 120 comprising the surface 104 and braze deposit 112 described above with a second component 122 comprising a mating surface 124 to form an assembly 126, where the braze deposit 112 contacts the mating surface 124. The assembly 126 is exposed to a bonding temperature and a compressive force, preferably in a controlled environment such as a vacuum or inert gas atmosphere, and the first component 120 is diffusion bonded to the second component 122. Diffusion bonding may be carried out using methods known in the art. Typically, the bonding temperature lies in a range from about 900° C. (˜1650° F.) to about 1275° C. (˜2325° F.), or from about 1000° C. (˜1830° F.) to about 1100° C. (˜2010° F.), depending on the alloy(s) being bonded.

Once metallurgically bonded together, the first component 120 and the second component 122 form a monolithic third component 128 comprising a homogeneous bonded interface 130 that may be substantially free of unwanted phases, defects, and/or porosity, as shown in FIG. 1F. In one example, the monolithic third component 128 comprises an airfoil, as described below. The first and second components 120,122 may have a single-crystalline or polycrystalline (e.g., equiaxed) microstructure. In other words, the first component 120 may be single-crystalline or polycrystalline, and the second component 122 may be single-crystalline or polycrystalline. When both the first and second components 120,122 have a single-crystalline structure, a directionally solidified microstructure may be obtained across the bonded interface 130. The method is applicable to nickel-base alloys, iron-base alloys, and titanium-base alloys, such as titanium aluminides.

Referring now to FIG. 2 , the first component 120 may be a coversheet 220 and the second component 122 may be a spar 222, which, when bonded together as described above, may form part or all of an airfoil with dual-wall cooling for use in a gas turbine engine. More specifically, the coversheet 220 may undergo the selective sintering process described above such that the braze powder is adhered only to predetermined locations on the surface 204. The spar 222 may include flow channels 216 alternating with raised surface features or “pedestals” 224 designed to mate with the braze deposit 212 on the surface 204 of the coversheet 220. The arrangement of the pedestals 224 and flow channels 216 shown in FIG. 2 is provided as an example only and is not intended to be limiting. Besides airfoils (e.g., turbine blades or vanes), the above-described method may be applicable to the fabrication of combustion liners, heat shields, and/or other gas turbine engine components.

To clarify the use of and to hereby provide notice to the public, the phrases “at least one of <A>, <B>, . . . and <N>” or “at least one of <A>, <B>, . . . <N>, or combinations thereof” or “<A>, <B>, . . . and/or <N>” are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, . . . and N. In other words, the phrases mean any combination of one or more of the elements A, B, . . . or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.”

While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible. Accordingly, the embodiments described herein are examples, not the only possible embodiments and implementations.

The subject-matter of the disclosure may also relate, among others, to the following aspects:

A first aspect relates to a method for selectively adhering braze powders to a surface, the method comprising: applying a braze powder to a surface, the braze powder being applied to a predetermined thickness or mass density; directing a laser beam onto the braze powder while the laser beam moves along a predetermined path relative to the surface, the laser beam selectively heating the braze powder along the predetermined path to sinter and bond the braze powder to the surface, thereby forming a braze deposit at one or more predetermined locations on the surface; and, after forming the braze deposit, removing excess braze powder not selectively heated by the laser from the surface.

A second aspect relates to the method of the first aspect, wherein applying the braze powder to the surface comprises spraying, scattering, or dusting the braze powder over the surface.

A third aspect relates to the method of the first or second aspect, wherein the braze powder is applied to the surface in an amount sufficient to achieve a mass density in a range from about 0.04 g/in² to about 0.25 g/in².

A fourth aspect relates to the method of any preceding aspect, wherein the predetermined path is a continuous path.

A fifth aspect relates to the method of any preceding aspect, wherein the predetermined path is a discontinuous path, the laser beam being operated intermittently while moving.

A sixth aspect relates to the method of any preceding aspect, wherein the surface is a discontinuous surface comprising surface regions separated by gaps, and wherein the braze deposit is formed on the surface regions.

A seventh aspect relates to the method of any preceding aspect, wherein the laser beam is generated by a laser selected from the group consisting of: gas laser, solid state laser, and fiber laser.

An eighth aspect relates to the method of any preceding aspect, wherein the laser beam is a pulsed laser beam.

A ninth aspect relates to the method of any preceding aspect, wherein the laser beam is a continuous laser beam.

A tenth aspect relates to the method of the any preceding aspect, wherein the laser beam is operated at a power level and a scan rate sufficient to sinter the braze powder without inducing melting.

An eleventh aspect relates to the method of any preceding aspect, wherein the braze powder along the predetermined path is selectively heated to a sintering temperature in a range from about 400° C. to about 800° C.

A twelfth aspect relates to the method of any preceding aspect, wherein removing the excess braze powder from the surface comprises vibrating, overturning, washing, brushing, or spraying the surface.

A thirteenth aspect relates to the method of any preceding aspect, wherein the surface is part of a first component comprising a metal alloy.

A fourteenth aspect relates to the method of any preceding aspect, wherein the first component comprises part of an airfoil, a combustion liner, or a heat shield of a gas turbine engine.

A fifteenth aspect relates to the method of any preceding aspect, wherein the braze powder comprises a nickel-based braze alloy, a titanium based-braze alloy, or an iron-based braze alloy.

A sixteenth aspect relates to a method of diffusing bonding comprising the method of any preceding aspect, wherein the surface is a first surface, and further comprising, after forming the braze deposit, assembling a first component comprising the first surface with a second component comprising a mating surface to form an assembly, the braze deposit on the first surface contacting the mating surface; and exposing the assembly to a bonding temperature and a compressive force, thereby diffusion bonding the first component to the second component to form a monolithic third component comprising a bonded interface.

A seventeenth aspect relates to the method of the sixteenth aspect, wherein the first component and the second component comprise a single-crystalline structure.

An eighteenth aspect relates to the method of the sixteenth or seventeenth aspect, wherein the first component and second component comprise a nickel-base alloy.

A nineteenth aspect relates to the method of the sixteenth through eighteenth aspects, wherein the first component comprises a coversheet and the second component comprises a spar, the monolithic third component comprising an airfoil for use in a gas turbine engine.

A twentieth aspect relates to a method of any of the sixteenth through the nineteenth aspects, wherein the bonding temperature is in a range from about 900° C. to about 1275° C.

In addition to the features mentioned in each of the independent aspects enumerated above, some examples may show, alone or in combination, the optional features mentioned in the dependent aspects and/or as disclosed in the description above and shown in the figures. 

What is claimed is:
 1. A method of diffusion bonding comprising: applying a braze powder comprising a braze alloy to a first surface; directing a laser beam onto the braze powder while the laser beam moves along a predetermined path relative to the first surface, the laser beam selectively heating the braze powder along the predetermined path to sinter and bond the braze powder to the first surface, the braze powder being heated to a sintering temperature that is below a solidus of the braze alloy, thereby forming a braze deposit at one or more predetermined locations on the first surface; and after forming the braze deposit, removing excess braze powder not selectively heated by the laser from the first surface, after forming the braze deposit, assembling a first component comprising the first surface with a second component comprising a mating surface to form an assembly, the braze deposit on the first surface contacting the mating surface; and exposing the assembly to a bonding temperature and a compressive force, thereby diffusion bonding the first component to the second component to form a monolithic third component comprising a bonded interface.
 2. The method of claim 1, wherein applying the braze powder to the first surface comprises spraying, scattering, or dusting the braze powder over the surface.
 3. The method of claim 1, wherein the braze powder is applied to the first surface in an amount sufficient to achieve a mass density in a range from about 0.04 g/in² to about 0.25 g/in².
 4. The method of claim 1, wherein the predetermined path is a continuous path.
 5. The method of claim 1, wherein the predetermined path is a discontinuous path, the laser beam being operated intermittently while moving.
 6. The method of claim 1, wherein the first surface is a discontinuous surface comprising surface regions separated by gaps, and wherein the braze deposit is formed on the surface regions.
 7. The method of claim 1, wherein the laser beam is generated by a laser selected from the group consisting of: gas laser, solid state laser, and fiber laser.
 8. The method of claim 1, wherein the laser beam is a pulsed laser beam.
 9. The method of claim 1, wherein the laser beam is a continuous laser beam.
 10. The method of claim 1, wherein the laser beam is operated at a power level and a scan rate sufficient to sinter the braze powder without inducing melting.
 11. The method of claim 1, wherein the braze powder along the predetermined path is selectively heated to a sintering temperature in a range from about 400° C. to about 800° C.
 12. The method of claim 1, wherein removing the excess braze powder from the surface comprises vibrating, overturning, washing, brushing, or spraying the first surface.
 13. The method of claim 1, wherein the first surface of the first component comprises a metal alloy.
 14. The method of claim 1, wherein the first component comprises part of an airfoil, a combustion liner, or a heat shield of a gas turbine engine.
 15. The method of claim 1, wherein the braze powder comprises a nickel-based braze alloy, a titanium-based braze alloy, or an iron-based braze alloy.
 16. The method of claim 1, wherein the first component and the second component comprise a single-crystalline structure.
 17. The method of claim 1, wherein the first component and second component comprise a nickel-base alloy.
 18. The method of claim 1, wherein the first component comprises a coversheet and the second component comprises a spar, the monolithic third component comprising an airfoil for use in a gas turbine engine.
 19. The method of claim 1, wherein the bonding temperature is in a range from about 900° C. to about 1275° C. 